A typical braking system for a vehicle includes a master cylinder and a hydraulic fluid reservoir which supplies fluid or accepts fluid from the cylinder depending upon fluid conditions (e.g. brake piston movement due to pad wear, fluid cooling, fluid heating, fluid leakage). The master cylinder and reservoir include a fluid conduit coupled therebetween such that fluid only flows between the cylinder and reservoir when the cylinders piston is within a predetermined range of motion (e.g. 5-10%) at the beginning of the pistons stroke. More specifically, the conduit connecting the cylinder and reservoir of a typical systems is connected to a cylinder port which opens to the inside of the cylinder along the predetermined range of motion of the piston at the beginning of its stroke. Accordingly, until the piston moves far enough to cover the port, fluid can flow from the cylinder to the reservoir and the fluid is not pressurized sufficiently to cause the brake actuator to generate the forces required for braking.
The conventional cylinder and reservoir arrangement described above typically requires precision tolerances on the placement of the cylinder port with respect to the piston backstop which defines the beginning of the piston stroke. Additionally, this arrangement requires that the piston and cylinder be fabricated with substantial precision. Furthermore, the range of piston motion between the edge of the piston seal and the cylinder port must be large enough to accommodate rubber swelling which occurs over time. As discussed above, the range of piston motion which is typically required before the piston seal covers and closes the cylinder port is about 5-10% of the pistons stroke. Accordingly, valuable fluid displacement (i.e. fluid displacement pressurized sufficiently to cause the brake actuator to generate forces required for braking) is wasted during piston movement before the cylinder port is covered.
In addition to having lost motion before valuable fluid displacement, conventional cylinder and reservoir arrangements require that the piston be returned to the beginning of its stroke to permit fluid flow between the cylinder and reservoir. More specifically, the piston must be moved such that the cylinder port is uncovered before fluid can flow between the cylinder and reservoir.
In view of the drawbacks of conventional master cylinder and fluid reservoir arrangements, it would be desirable to provide an improved arrangement which reduces or eliminates wasted piston motion during braking. It would also be desirable to provide an arrangement which permits fluid flow between the cylinder and reservoir after braking force is removed from the piston irregardless of the home position of the piston.